Majoru Oakheart said:However, at the very least, we can assume that if an enemy can attack someone, then hit, then take a free action to grapple that if an enemy attacks someone, hits, then you can declare an immediate action between hitting and damage being rolled.
There are no actions allowed in the game between hitting and damage being rolled. It is one action, not two. Actions are atomic units. You can do an action during another action, but you cannot split up an action into different parts and than make a determination when part one is done and before part two is done to do something else.
You can declare the immediate action when the attack is declared, but if you declare it after the "to hit roll" is made (presumably because you see if it hit or not), you cannot declare your immediate action before the damage is actually rolled and assigned.
Granted, there are some specific actions which appear to allow this such as using an Action Point. But, it is explicitly called out in the rules that you can do this. Even here, you do not get to declare to use an Action point before finding out if the Saving Throw is made or not. You roll the dice, declare an Action point or not, and then determine if the save made or not.
But, this is an explicit exception to the rules. Once you roll the "to hit" die, nothing can interrupt the damage dice unless there is a specific rule, spell, etc. that explicitly allows you to do so.